Modem Always-On;
and Network Element Dial-Out Prevention
This feature enables a TTY X.28-configured line to interpret characters from network elements without
first having to receive a RING, CTS, or DSR signal. The feature also allows you to require that a DSR
signal be received by the line before the router will interpret characters from network elements or the
network. Finally, this feature enables you to have the TTY line prevent network elements from sending
characters until an appropriate X.25 switched virtual circuit (SVC) has been set up.
History for the Modem Always-On and Network Element Dial-Out Prevention Feature
Release
Modification
12.3(11)YN
This feature was introduced.
12.4(4)T
This feature was integrated into Cisco IOS 12.4(4)T.
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Contents
•
Prerequisites for Modem Always-On and NE Dial-Out Prevention, page 2
•
Restrictions for Modem Always-On and NE Dial-Out Prevention, page 2
•
How to Configure Modem Always-On, page 3
•
How to Prevent NE Dial-Out, page 7
•
Configuration Example for Modem Always-On and NE Dial-Out Prevention, page 8
•
Command Reference, page 10
•
Glossary, page 15
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Copyright © 2005 Cisco Systems, Inc. All rights reserved.
Modem Always-On; and Network Element Dial-Out Prevention
Prerequisites for Modem Always-On and NE Dial-Out Prevention
Prerequisites for Modem Always-On and NE Dial-Out
Prevention
•
Because legacy PAD provides insufficient support for Modem Always-On, you must enter the
autocommand x28 command during its configuration. You will see this illustrated in detail in the
configuration sections further on in this document.
•
For NE Dial-Out Prevention, the TTY line being configured must run an X.28 user emulation
session.
Restrictions for Modem Always-On and NE Dial-Out Prevention
This feature is supported only for X.28 PAD connections.
Information About Modem Always-On and NE Dial-Out
Prevention
When the modem always-on command has taken effect, the TTY line can interpret characters received
from network elements without waiting for a RING, CTS, or DSR signal to arrive. (Similarly, when the
modem printer always-on command has taken effect, the TTY line can interpret characters received
from network elements without waiting for a CTS signal to arrive). These arrangements can be useful,
for example, when you need to run an X.28 user emulation session on a TTY line that has only TX, RX,
and Ground signals.
However, until an appropriate X.25 SVC has also been set up, all characters received through the TTY
line from the network element will be dropped.
Also, because some network elements might then be capable of sending characters without first dialing
out or receiving an inbound call, the command x28 no-outgoing has become available. With this
command you can prevent the network element from dialing out (until an appropriate X.25 SVC has been
set up).
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How to Configure Modem Always-On
How to Configure Modem Always-On
If you want the router to wait for an incoming DSR signal before it will interpret network element
characters, use the modem printer always-on command. However, if you prefer that the router begin
interpreting network element characters without waiting for a DSR signal (nor a RING or CTS signal)
use the modem always-on command.
•
Requiring a DSR Signal (”modem printer always-on“), page 3
•
Requiring no DSR, CTS, or RING Signal (”modem always-on“), page 4
Requiring a DSR Signal (”modem printer always-on“)
Prerequisites
The line must be configured with "autocommand x28".
SUMMARY STEPS
1.
enable
2.
configure terminal
3.
line line_number
4.
autocommand x28
5.
modem printer [delay | always-on [delay] ]
6.
exit
DETAILED STEPS
Step 1
Command or Action
Purpose
enable
Enables privileged EXEC mode.
•
Enter your password if prompted.
Example:
Router> enable
Step 2
configure terminal
Enters global configuration mode.
Example:
Router# configure terminal
Step 3
line [aux | console | tty | vty] line-number
[ending-line-number]
Identifies a specific line for configuration, and enters line
configuration mode.
Example:
Router(config)# line 48
Step 4
autocommand x28
Makes this line available to receive calls coming from the
network via the router.
Example:
Router(config-line)# x28 autocommand
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How to Configure Modem Always-On
Step 5
Command or Action
Purpose
modem printer always-on [delay | always-on
[delay] ]
Enables the line to interpret characters received from
network elements after it receives a DSR signal. The line
need not wait for a CTS signal.
Example:
Router(config-line)# modem printer always-on
Step 6
Moves back into global configuration mode.
exit
Example:
Router# exit
Example
Router> enable
Router# configure terminal
Enter configuration commands, one per line.
Router(config)# line 48
Router(config-line)# autocommand x28
Router(config-line)# modem printer always-on
Router(config-line)# exit
Router(config)#
End with CNTL/Z.
What to Do Next
If you want to see confirmation of the new ‘modem-on’ state of the line, use the show line command.
The line’s modem is displayed as "printer" (in the 5th column), its Capability as "Modem...Always on"
(8th line), and its state is shown as "Ready" (9th line):
Router# show line tty 48
Tty Typ
Tx/Rx
A Modem
Roty AccO AccI
*
48 TTY
9600/9600 - printer
1
-
Uses
0
Noise
0
Overruns
0/0
Line 48, Location: "", Type: ""
Length: 24 lines, Width: 80 columns
Baud rate (TX/RX) is 9600/9600, no parity, 2 stopbits, 8 databits
Status: Ready, Modem Signals Polled
Capabilities: Modem CTS-Required, Always on
Modem state: Ready
Modem hardware state: CTS* DSR* DTR RTS
. . .
Requiring no DSR, CTS, or RING Signal (”modem always-on“)
Prerequisites
The line must be configured with "autocommand x28".
SUMMARY STEPS
1.
enable
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How to Configure Modem Always-On
2.
configure terminal
3.
line line_number
4.
autocommand x28
5.
modem always-on
6.
exit
DETAILED STEPS
Step 1
Command or Action
Purpose
enable
Enables privileged EXEC mode.
•
Enter your password if prompted.
Example:
Router> enable
Step 2
configure terminal
Enters global configuration mode.
Example:
Router# configure terminal
Step 3
line [aux | console | tty | vty] line-number
[ending-line-number]
Identifies a specific line for configuration, and enters line
configuration mode.
Example:
Router(config)# line 35
Step 4
autocommand x28
Makes this line available to receive calls coming from the
network via the router.
Example:
Router(config-line)# x28 autocommand
Step 5
modem always-on
Example:
Enables the line to interpret characters received from
network elements without waiting for a RING, CTS, or
DSR signal.
Router(config-line)# modem always-on
Step 6
Moves back into global configuration mode.
exit
Example:
Router# exit
Example
Router> enable
Router# configure terminal
Enter configuration commands, one per line.
Router(config)# line 97
Router(config-line)# autocommand x28
Router(config-line)# modem always-on
Router(config-line)# exit
Router(config)#
End with CNTL/Z.
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How to Configure Modem Always-On
What to Do Next
If you want to see confirmation of the new ‘modem-on’ state of the line, use the show line command. In
the following sample output display, line 35 has been configured with the feature. (Modem status is given
in the fifth column.)
Router# show line
Tty Typ
Tx/Rx
A Modem Roty AccO AccI
*
0 CTY
33 TTY
9600/9600 34 TTY 115200/115200- inout
1
*
35 TTY
9600/9600 - always-on 1
36 TTY
9600/9600 -
Uses
0
0
0
0
0
Noise
0
0
0
0
0
Overruns
0/0
0/0
0/0
0/0
0/0
Int
-
You can also use the show line command to display information only about the line you configured. In
that case, the line’s modem state will be displayed as "Ready":
Router# show line 35
Tty Typ
Tx/Rx
*
35 TTY
9600/9600
A Modem Roty AccO AccI
Uses
Noise Overruns
- always-on
1
0
0
0/0
Line 35, Location: "", Type: ""
Length: 24 lines, Width: 80 columns
Baud rate (TX/RX) is 9600/9600, no parity, 2 stopbits, 8 databits
Status: Ready, Active, No Exit Banner
Capabilities: Modem RI is CD, Round Robin Selection
Modem state: Ready
Modem hardware state: noCTS noDSR DTR RTS
. . .
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How to Prevent NE Dial-Out
How to Prevent NE Dial-Out
Prerequisites
The TTY line must already have been configured for X.28 user emulator mode.
SUMMARY STEPS
1.
enable
2.
x28 no-outgoing
DETAILED STEPS
Step 1
Command or Action
Purpose
enable
Enables privileged EXEC mode.
•
Enter your password if prompted.
Example:
Router> enable
Step 2
x28 no-outgoing
Configures X.28 user emulation mode to prevent network
elements from dialing out.
Example:
Router# x28 no-outgoing
Caution
Do not use the x28 no-outgoing command on the console, because that will lock the console. Then, to
unlock it, you will have to log in from a different TTY (or a VTY), and if such a line is not available,
you will have to reload the router.
Examples
The following example configures X.28 user emulation mode for all TTY lines on the router to prevent
network elements from calling out:
Router# x28 no-outgoing
The following example configures X.28 user emulation mode only on TTY line 33, in autocommand, to
prevent network elements from calling out through that line:
Router# configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Router(config)# line 33
Router(config-line)# autocommand x28 no-outgoing
Router(config-line)# exit
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Configuration Example for Modem Always-On and NE Dial-Out Prevention
Configuration Example for Modem Always-On and NE Dial-Out
Prevention
Router> enable
Router# configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Router(config)# line 35
Router(config-line)# modem always-on
Router(config-line)# autocommand x28 no-outgoing
Router(config-line)# end
Router# show line 35
Tty Typ
Tx/Rx
A Modem
Roty AccO AccI
Uses
Noise Overruns
*35 TTY
9600/9600
- always-on
1
0
0
0/0
Line 35, Location: "", Type: ""
Length: 24 lines, Width: 80 columns
Baud rate (TX/RX) is 9600/9600, no parity, 2 stopbits, 8 databits
Status: Ready, Active, No Exit Banner
Capabilities: Modem RI is CD, Round Robin Selection
Modem state: Ready
Modem hardware state: noCTS noDSR DTR RTS
Rotary address 45678
Special Chars: Escape Hold Stop Start Disconnect Activation
^^x
none
none
Timeouts:
Idle EXEC
Idle Session
Modem Answer Session
00:10:00
never
none
Idle Session Disconnect Warning
never
Login-sequence User Response
00:00:30
Autoselect Initial Wait
not set
Modem type is unknown.
Session limit is not set.
Time since activation: 00:04:27
Editing is enabled.
History is enabled, history size is 20.
DNS resolution in show commands is enabled
Full user help is disabled
Allowed input transports are pad.
Allowed output transports are pad v120 telnet rlogin.
Preferred transport is telnet.
Automatically execute command "x28 no-outgoing"
No output characters are padded
No special data dispatching characters
Router#
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Modem Always-On; and Network Element Dial-Out Prevention
Configuration Example for Modem Always-On and NE Dial-Out Prevention
Technical Assistance
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Command Reference
Command Reference
This section documents new and modified commands only.
•
modem always-on
•
modem printer
•
x28 no-outgoing
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modem always-on
modem always-on
To make a TTY line always ready to interpret characters from network elements, use the modem
always-on command in line configuration mode. To disable, use the no form of this command.
modem always-on
no modem always-on
Syntax Description
No syntax.
Command Default
Off is the default condition.
Command Modes
Line configuration mode.
Command History
Release
Modification
12.3(11)YN
This command was introduced.
12.4(4)T
This command was integrated into the T train.
Usage Guidelines
To make the line available to receive calls coming from the network via the router, you must also
configure the line with "autocommand x28".
Examples
The following example makes TTY line 97 able to interpret characters received from network elements,
without having to wait for other incoming signals:
Router(config)# line 97
Router (config-line)# modem always-on
Related Commands
Command
Description
modem printer [delay| always-on [delay]]
Configures a line to receive a Data Set Ready (DSR)
signal before it will interpret incoming characters from
a network element.
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modem printer
modem printer
To configure a line to require receipt of a Data Set Ready (DSR) signal, use the modem printer
command in line configuration mode. Use the no form of this command to require the Clear to Send
(CTS) signal instead.
modem printer [delay | always-on [delay] ]
no modem printer
Syntax Description
delay
Causes router to delay assertion of the data terminal ready (DTR) signal until
a network connection has been established.
always-on
Makes the line ready to interpret characters from network elements.
delay
While the always-on option is operating, this delays DTR signal assertion
until a network connection has been established.
Command Default
No modem control.
Command Modes
Line configuration mode.
Command History
Release
Modification
11.1
This command was introduced.
12.2T
The ‘delay’ option was added.
12.3(11)YN
The ‘always-on’ option was added.
Usage Guidelines
Examples
1.
By using DSR as the modem control signal, this command leaves the CTS (Clear to Send) signal
free for use with hardware flow control. You therefore can configure hardware flow control
concurrently. [Although the modem dialin command supports modems concurrently with hardware
flow control, the other auxiliary modem control options for printers, such as modem cts-required,
use CTS instead of DSR/CD, as the carrier detect (CD) signal.]
2.
To make the line available to receive calls coming from the network via the router with the alwayson keyword, you must also configure that line with "autocommand x28".
The following example configures a line to send a DSR signal to the modem:
Router(config)# line 5
Router (config-line)# modem printer
The following example configures a line to become ready to interpret characters from network elements
when it receives a DSR signal:
Router(config)# line 5
Router (config-line)# modem printer always-on
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modem printer
Related Commands
Command
Description
flowcontrol
Sets the method of data flow control between the router and a terminal
or other serial device.
modem always-on
Makes a TTY line always ready to interpret characters from network
elements, without waiting to receive a DSR, RING or CTS signal.
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x28 no-outgoing
x28 no-outgoing
To configure X.28 user emulation mode to prevent a network element from dialing out, use the x28
no-outgoing command in user EXEC or privileged EXEC mode. To disable, use the no form of this
command.
x28 no-outgoing
no x28 no-outgoing
Syntax Description
No syntax.
Command Default
The default condition is not to block network elements from calling out.
Command Modes
Command History
Usage Guidelines
Examples
1.
User EXEC or privileged EXEC mode when the command is used for all TTY lines connected to the
router and configured in X.28 emulation mode.
2.
Line configuration mode when the command is used with autocommand for a particular TTY line
configured for X.28 emulation mode.
Release
Modification
12.3(11)YN
This command was introduced.
12.4(4)T
This command was integrated into the T train.
1.
Usually the no-outgoing configuration is used with autocommand on a per-line basis (as shown in
the second example, below).
2.
WARNING: Do not use the x28 no-outgoing command on the console -- because that will lock the
console. Then, to unlock it, you will have to log in from a different TTY (or a VTY), and if such a
line is not available, you will have to reload the router.
The following example configures X.28 user emulation mode on all of this router’s TTY lines to prevent
network elements from calling out:
Router# x28 no-outgoing
The following example configures X.28 user emulation mode only on TTY line 33, in autocommand, to
prevent network elements from calling out through that line:
Router# configure terminal
Enter configuration commands, one per line.
Router(config)#line 33
Router(config-line)#autocommand x28 no-outgoing
Router(config-line)#exit
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End with CNTL/Z.
Modem Always-On; and Network Element Dial-Out Prevention
Glossary
Glossary
CTS—Clear To Send. The signal sent by a DCE (data communications equipment; modem) when it is
ready to receive data.
DSR—Data Set Ready. The signal sent by a modem (DCE) once it is powered up and ready.
DTR—Data Terminal Ready. The signal sent by a DTE (data terminal equipment; computer) when it is
ready to receive data.
SVC—Switched Virtual Circuit. The path through an X.25 network that is established at call set-up time.
Note
See Internetworking Terms and Acronyms for terms not included in this glossary.
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Glossary
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